Magnetic stimulation methods and devices for therapeutic treatments

ABSTRACT

Methods and devices producing time varying magnetic field have therapeutic uses. The device contains a coil made of insulated wires, an energy storage device, an energy source and a switch. The coil is flexibly attached in a case. The device has at least one blower for cooling the coil. The methods and devices can be used in for example in physiotherapy, neuropsychiatric therapy, aesthetic therapy, urology or urogynecology.

BACKGROUND OF THE INVENTION

Devices and methods generating magnetic pulses have long been used formedical treatments. A time-varying magnetic field induces electriccurrents in the patient's body, which may provide similar effect aselectrotherapeutic treatment. With sufficient intensity, duration andrepetition rate, the induced electrical currents may evoke actionpotential of neurons, muscle fibers and endocrine cells. The advantageof the methods using magnetic field compared with electrotherapeuticalmethods is that changing magnetic field therapy does not require contactwith the patient and can be performed through clothing. With magneticfield treatments, the stimulating signal does not pass through the skin.Rather, the electrical currents are induced directly in the stimulatedtissue. This increases stimulation focus and eliminates unwanted sideeffects of the therapy (e.g. skin irritation). Using a sufficientlylarge magnetic flux density and/or repetition rate, it is possible tostimulate various tissues without need of invasive methods.

SUMMARY OF THE INVENTION

A time varying magnetic field may be used to treat variety disorders andinjuries of muscle, nerve and connective tissue. It may also be usedalso in physiotherapy, aesthetic therapy, urology, urogynecology,psychiatry, neurology and neurophysiology for therapy anddiagnosis/prognosis.

A device for time variable magnetic field generation may include anenergy source, an energy storage device, a switching circuit, a coil andpossibly a core. The energy storage device accumulates tens of Joules ofenergy and the magnetic flux density induced by the coil is in the rangeof tenths of a Tesla to about one Tesla.

Existing devices have low efficiency and they waste energy, which limitstheir use. Eddy currents induced within the coil create engineeringchallenges. Existing devices contain coils which are made of metallicstrips, electric wires or hollow conductors. Since the therapy requireslarge currents, significant losses are caused by induced eddy currentswithin the coil. Eddy currents lead to production of unwanted heat andtherefore there is need to sufficiently cool the coil. Also, the energysource must be protected during reverse polarity of resonance. Thisrequires using protective circuits which consume significant amounts ofenergy.

Due to low efficiency, existing devices may not achieve repetition ratesof magnetic pulses above one hundred Hertz, as may be needed to producea magnetic flux density sufficient for acting on neurons, muscle fibersand/or endocrine cells (e.g. at least partial muscle contraction). Usingexisting devices, interruptions during therapy or between therapies areoften necessary to avoid overheating the device.

The present methods and devices as described below produce a timevarying magnetic field for patient treatment which better optimizesenergy use, increases the effectiveness of the treatments and provide anew treatment. The magnetic pulses may be generated in monophasic,biphasic or polyphasic regimes. In a first aspect, the device has one ormore coils; a switch; an energy storage device and a connection to anenergy source. The coil may be made of insulated wires with a conductordiameter less than 3 mm even more preferably less than 0.5 mm and mostpreferably less than 0.05 mm. Smaller diameter and individual insulationof the wires significantly reduces self-heating of the coil andtherefore increase efficiency of magnetic stimulation device. The coilmay be flexibly attached in a casing of device. The casing may comprisea blower or blowers which ensure cooling of the coil.

Space between the insulated wires may be filled with a solid material soas to reduce the noise caused by vibrations. The coil is connected withan energy storage device which serves as a storage of energy.

The switch can be any kind of switch such as diode, MOSFET, JFET, IGBT,BJT, thyristor or a combination of them. The switch can be connected inparallel to the coil and the energy storage device, to eliminatereversal polarity of high voltage on the terminals of the energy sourcein the second half of the resonant effect. Therefore there is no needfor additional protective circuits to protect the energy source from thenegative voltage. Electric losses associated with such protectivecircuits are avoided. Energy use is reduced. The voltage drop in theenergy storage device between first and second oscillation maximumduring resonance is also reduced. Via the lower voltage drop, higherrepetition rates of magnetic pulses and higher magnetic flux density maybe achieved for treatment of the patient.

The coil of the magnetic stimulation device may be flexibly attached tocasing of the device. The blower or blowers may be arranged to blow airon both sides of coil. Optionally, the coil may be a flat type coil.

As used here “continual therapy” and “continual magnetic stimulation”means therapy where the set of the magnetic flux density andfrequency/repetition rate of magnetic pulses does not lead to exceedingof the operating temperature 43° C. on the casing of the deviceoperating in an ambient temperature of 30° C. regardless of the durationof therapy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross section view of a coil winding.

FIG. 2 is an illustrative embodiment of cross-section of the magneticapplicator.

FIG. 3 is an illustrative embodiment of a casing of the magneticapplicator.

FIGS. 4A and 4B illustrates circuit for providing high power pulses to astimulating coil.

FIG. 5 is a graph showing voltage drop in the energy storage device.

DETAILED DESCRIPTION

FIG. 1 illustrates a cross section of winding of a coil for a magneticstimulation device. The coil may be constructed from litz-wire, whereineach wire is insulated separately. Each individual conductor is coatedwith non-conductive material so the coil constitutes multiple insulatedwires. Unlike existing magnetic coil conductors, the present coil is notmade of bare wire e.g. litz-wire without insulation, or conductivetapes, conductive strips, or copper pipe with hollow inductors. Theinsulation of wires separately is a substantial improvement, since thisleads to a significant reduction of the induced eddy currents. Powerloss due to eddy currents, per single wire, is described by Equation 1below. The small diameter wires of the present coil significantly reduceself-heating of the coil and therefore increases efficiency of thepresent magnetic stimulation device:

$\begin{matrix}{{P_{EDDY} = \frac{\pi^{2} \cdot B_{P}^{2} \cdot d^{2} \cdot f^{2}}{6 \cdot k \cdot \rho \cdot D}},} & {{Eq}.\mspace{11mu} 1}\end{matrix}$where: P_(EDDY) is power loss per unit mass (W·kg⁻¹); B_(p) is the peakof magnetic field (T); f is frequency (Hz); d is the thickness of thesheet or diameter of the wire (m); k is constant equal to 1 for a thinsheet and 2 for a thin wire; ρ is the resistivity of material (Ω·m); Dis the density of material (kg·m³).

The individual insulation of each wire reduces eddy currents. Theindividually insulated wires may be wound either one by one or in abundle of individually insulated wires so as to form a coil, which willserve as a magnetic field generator. The coil provides an improvement inthe efficiency of energy transfer in the LC resonant circuit and alsoreduces or eliminates unwanted thermal effects.

The coil may have a planar coil shape where the individually insulatedwires may have cross-section wires with conductor diameter less than 3mm even more preferably less than 0.5 mm and most preferably less than0.05 mm. The wires are preferably made of materials with higher densityand higher resistivity e.g. gold, platinum or copper. The diameters ofthe single wires should be minimal. On the other hand the total diametershould be maximal because of inverse proportion between thecross-section of all wires forming the coil and the electricalresistance. Therefore the ohmic part of the heat is then lower. Eq. 2describes power loss of the coil:

$\begin{matrix}{P_{R} = \frac{\rho \cdot \frac{l}{S} \cdot I^{2}}{m}} & {{Eq}.\mspace{11mu} 2}\end{matrix}$Where: P_(R) is the power loss heat dissipation (W);ρ is the resistance(Ω·m); l is the length of wire (m); S is the surface area (m²); I is thecurrent (A) and m is 1 kg of wire material.

Total power loss is (Eq.3):P _(TOT) =P _(EDDY) +P _(R),  Eq. 3Where: P_(TOT) is the total power losses (W·kg⁻¹); P_(EDDY) is the powerdissipation of eddy currents (W·kg⁻¹); P_(R) is the power loss heatdissipation (W·kg⁻¹).

Dynamic forces produced by current pulses passing through the wires ofthe coil cause vibrations and unwanted noise. The individual insulatedwires of the coil may be impregnated under pressure so as to eliminateair bubbles between the individual insulated wires. The space betweenwires can be filled with suitable material which causes unification,preservation and electric insulation of the system. Suitable rigidimpregnation materials like resin, and elastic materials like PTE can bealso used. With the coil provided as a solid mass, the vibrations andresonance caused by movements of the individual insulated wires aresuppressed. Therefore noise is reduced.

The coil may be attached to the case of the applicator, such as a handheld applicator of the magnetic stimulation device; built-in applicatorin e.g. chair, bed; or stand-alone applicator e.g. on mechanicalfixture. The attachment may be provided by an elastic material e.g.,silicone, gum; or other flexible manner. Connection with the coil of theapplicator's case can be ensured by several points. The severalfastening points ensure the connection of the coil to the casing byflexible material so that the main part of the coil and the main part ofthe casing of applicator are spaced apart. The spacing should be atleast 0.1 mm so that air can easily flow. The gap between the coil andthe casing can be used either for spontaneous or controlled cooling. Thecoil may optionally be connected to the case of the applicator by onlyone fastening point. The fastening points eliminate vibrations of wireswhich could be transferred to housing of the applicator and thereforereduce noise of the magnetic stimulation device.

FIG. 2 is a cross-section of the magnetic applicator which allows betterflow on the lower and upper sides of the coil and thus more efficientheat dissipation. The magnetic stimulation device includes a coil 10,the circuit wires 11 and the fastening points 12 for connection of thecoil to the casing of the applicator (not shown). The fastening points12 are preferably made of flexible material however the rigid materialmay be used as well. The fastening points 12 may be located on the outercircumferential side of the coil. However, alternatively it is possibleto put these fastening points to a lower or upper side of the coil.

The fastening points 12 connect the coil to the case of the applicatorin at least one point. The fastening points 12 maintain the coil and themain part of the case of the applicator spaced apart so that fluid(which may be air or any liquid) can flow between them. At least oneblower 13 can be placed around the circumference of the coil, orperpendicular to the coil. The blower can be any known kind of devicefor directing the fluid e.g. outer air directed into the case of theapplicator. This arrangement of the blower allows air to bypass the coilfrom upper and lower (patient's) sides. In still another embodiment theouter air can be cooled before directing into the case. The blower canhave an inlet placed around the circumference of the coil for injectingair, to remove heat from the coil. A connecting tube (not shown) canensure connection of the applicator 14 with the energy source and/orcontrol unit of magnetic stimulation device. The connecting tube mayalso contain a conduit of the fluid.

The arrows 15 indicate the air flow through the applicator 14. Thisarrangement of the blower allows the air to bypass the coil from upperand lower (patient's) side. Outlet may be preferably placed on upperside of the casing. By placing the blower around the circumference ofthe coil instead of on the top/below the coil, the blower 13 does notinterfere with the magnetic flux peak and therefore its lifespan andreliability is increased.

FIG. 3 is an illustrative embodiment of a casing of the magneticapplicator. The overview drawing contains casing itself 16, which mightcontain an outlet 17 preferably placed on upper side of the casing 16. Aconnecting tube 18 may not only ensure connection of the applicator withthe energy source and/or control unit of magnetic stimulation device,but also connection to a source of the fluid; however the conduit of thefluid 19 may also be connected separately.

FIG. 4A and FIG. 4B illustrate circuits for providing high power pulsesto the stimulating coil. FIG. 4A shows a circuit for providing highpower magnetic pulses. FIG. 4B shows a circuit for providing high powerpulses.

Existing magnetic stimulation devices achieve magnetic flux density of afew tenths to several Teslas. To achieve this level of magnetic fluxdensity, the energy source used generates sufficient voltage. Thisvoltage can reach thousands of volts. In FIG. 4A the circuits forproviding high power pulses to the stimulating coil contain a seriesconnection to the switch 22 and the coil 21. The switch 22 and the coil21 together are connected in parallel with an energy storage device 20.The energy storage device 20 is charged by the energy source 23 and theenergy storage device 20 then discharges through the switching device 22to the coil 21.

During second half-period of LC resonance, the polarity on the energystorage device 20 is reversed in comparison with the energy source 23.In this second half-period, there is a conflict between energy source23, where voltage on positive and negative terminals is typicallythousands of Volts. The energy storage device 20 is also charged to thepositive and negative voltage generally to thousands of Volts. As aresult, there is in the circuit, consequently, twice the voltage of theenergy source 23. Hence the energy source 23 and all parts connected inthe circuit are designed for a high voltage load. Therefore, theprotective resistors and/or protection circuitry 24 must be placedbetween energy source 23 and energy storage device 20. As a result alarge amount of energy is transformed to undesired heat in theprotective resistors and/or protection circuitry 24.

FIG. 4B shows a circuit for providing high power pulses for improvedfunction of the magnet stimulation device. The coil 31 and an energystorage device 30 are connected in series and disposed in parallel tothe switch 32. The energy storage device 30 is charged through the coil31. To provide an energy pulse, controlled shorting of energy source 33takes place through the switch 32. In this way the high voltage load atthe terminals of the energy source 33 during the second half-period ofLC resonance associated with known devices is avoided. The voltage onthe terminals of energy source 33 during second half-period of LCresonance is a voltage equal to the voltage drop on the switch 32.

The switch 32 can be any kind of switch such as diode, MOSFET, JFET,IGBT, BJT, thyristor or their combination. Depending on the type ofcomponent the load of energy source 33 is reduced to a few Volts, e.g.,1-10 volts. Consequently, it is not necessary to protect the energysource 33 from a high voltage load, e.g., thousands of Volts. The use ofprotective resistors and/or protection circuits is reduced oreliminated. The present designs simplify the circuits used, increaseefficiency of energy usage and provide higher safety.

FIG. 5 show an exponential voltage drop in the energy storage device.Energy savings during time-varying magnetic therapy may be characterizedby reduced voltage drop in the energy storage device between the first,second and subsequent maximums of the resonant oscillation. Themagnitude of the individual voltage oscillations is exponentiallydampened up to establishing the energy balance. This allows increasingthe maximum possible frequency/repetition rate of magnetic pulses, sincethe frequency/repetition rate is dependent on the speed with which it ispossible to recharge the energy storage device. Since the energy storagedevice is recharged by the amount of energy loss during the previouspulse, it is possible to increase the frequency/repetition rate of thedevice up to hundreds of magnetic pulses per second without the need toincrease the input power. The voltage drop between any of the successiveamplitudes is not higher than 21%, even more preferably not higher than14% and most preferably not higher than 7%.

The device can be used for treatment/successive treatments in continual,interrupted or various duty cycle regime. The duty cycle may be higherthan 10%, which means interrupted regime with the ratio up to 1 activeto 9 passive time units. The ratio may possibly change during thetherapy. The device enables operation defined by the peak to peakmagnetic flux density on the coil surface at least 3 T, more preferablyat least 2.25 T, most preferably at least 1.5 T at repetition ratesabove 50 Hz, more preferably at repetition rates above 60 Hz, even morepreferably at repetition rates above 70, most preferably at repetitionrates above 80 Hz with treatment/successive treatments lasting severalseconds or longer, for example, for at least 5, 10, 30, 60, 120 or 240seconds, or longer. The total power consumption is below 1.3 kW and thewidth of pulses is in the range of hundreds of μs.

The device enables achieving repetition rates above 100 Hz, morepreferably repetition rates above 150 Hz, most preferably repetitionrates above 200 Hz with the magnetic flux density providing atherapeutic effect on neurons and/or muscle fibers and/or endocrinecells (e.g. at least partial muscle contraction, action potential incell). Based on achievement of repetition rates in order of few hundredsthe device also enables assembling the magnetic pulses into the variousshapes (e.g. triangular, rectangular, exponential), with the shapewidths from 6 ms to several seconds or longer.

Thus, novel devices and methods have been shown and described. Variouschanges and substitutions may be made without departing from the spiritand scope of the invention. The invention, therefore, should not belimited except to the following claims and their equivalents.

The invention claimed is:
 1. A magnetic stimulation device, comprising:a connection to an energy source; a first coil and a second coil,wherein the first coil is configured to generate a first time-varyingmagnetic field and the second coil is configured to generate a secondtime-varying magnetic field; a switching device coupled to the energysource; an energy storage device coupled to the switching device; thefirst coil disposed within a casing of a hand-held applicator andcoupled to at least one of the energy storage device and the switchingdevice, wherein the first coil comprises a plurality of litz wires, andwherein each litz wire is separately insulated; wherein the first coilis planar, wherein the plurality of litz wires are impregnated, andwherein the first coil is coupled to the casing of the applicator by atleast one fastening point such that the first coil is spaced apart fromthe casing by a distance of at least 0.1 mm; and a cooling deviceconfigured to cool the first coil and the casing of the applicator suchthat a temperature of the casing of the applicator does not exceed 43°C., wherein the energy storage device is configured to be charged viathe connection to the energy source, and wherein the switching device isconfigured to enable a discharge of the charged energy storage device tothe first coil to generate the first time-varying magnetic field.
 2. Themagnetic stimulation device of claim 1, wherein the time-varyingmagnetic field has a magnetic flux density of at least 1.5 Tesla on asurface of the coil.
 3. The magnetic stimulation device of claim 2,wherein the applicator is attached to a mechanical fixture.
 4. Themagnetic stimulation device of claim 2, wherein the switching device iscoupled in parallel to a serial connection of the first coil and theenergy storage device.
 5. The magnetic stimulation device of claim 1,wherein the cooling device comprises a blower, wherein the blower isconfigured to direct a fluid to the applicator so that the first coiland the casing of the applicator is cooled by the fluid, and wherein theblower is disposed on the casing of the applicator around acircumference of the first coil.
 6. The magnetic stimulation device ofclaim 5, wherein the casing of the applicator comprises an air outlet onan upper side of the casing of the applicator, and wherein the upperside of the casing of the applicator is configured to be positionedfarther from a patient than a lower side of the casing of theapplicator.
 7. The magnetic stimulation device of claim 1, wherein aconnecting tube is configured to couple the applicator to a source of afluid.
 8. The magnetic stimulation device of claim 7, further comprisinga conduit configured to direct the fluid to the coil, wherein theconduit is coupled to the casing of the applicator around acircumference of the casing of the applicator.
 9. A magnetic stimulationdevice, comprising: a control unit electrically coupled to an energysource; a switching device coupled to the control unit; and a coildisposed within a casing of an applicator and coupled to an energystorage device, the coil comprising a litz wire, wherein the energysource is configured to charge the energy storage device, wherein thecharged energy storage device is configured to discharge energy to thecoil to generate a time-varying magnetic field, wherein the coil isconfigured to be cooled, wherein the coil comprises a conductor with adiameter of less than 3 mm, wherein the coil is attached to the casingof the applicator by at least one flexible fastening point, and whereinthe applicator is coupled to the energy source via a connecting tube.10. The magnetic stimulation device of claim 9, wherein the connectingtube is configured to direct a cooling media from a fluid source to theapplicator.
 11. The magnetic stimulation device of claim 9, wherein thecoil is a planar type coil.
 12. The device of claim 9, wherein the litzwire is impregnated.
 13. The magnetic stimulation device of claim 9,further comprising a blower disposed on the casing around on acircumference of the coil.
 14. The magnetic stimulation device of claim9, wherein the coil is configured to be cooled by an air flow over anupper side and a lower side of the coil, between the casing and thecoil.
 15. The magnetic stimulation device of claim 9, wherein theconductor is coated with a non-conductive material.
 16. The magneticstimulation device of claim 9, wherein the conductor comprises at leastone of gold, platinum, or copper.
 17. A magnetic stimulation device,comprising: an energy storage device; and a coil disposed in a casing ofan applicator and coupled to the energy storage device, wherein the coilis attached to the casing by a flexible fastening point configured tospace the coil apart from the casing, wherein the energy storage deviceis configured to be charged by an energy source, wherein, after beingcharged, the energy storage device is configured to discharge energy tothe coil to generate a plurality of pulses of a time-varying magneticfield, and wherein the flexible fastening point is configured to enablea cooling fluid to flow between the coil and the casing.
 18. Themagnetic stimulation device of claim 17, wherein the coil is a planartype coil.
 19. The magnetic stimulation device of claim 17, furthercomprising a blower disposed on the casing around a circumference of thecoil.
 20. The magnetic stimulation device of claim 17, wherein thecooling fluid comprises air, and wherein the device is configured suchthat the air is flowed over an upper side of the coil and a lower sideof the coil.
 21. The magnetic stimulation device of claim 17, whereinthe energy storage device is in a serial connection with the coil. 22.The magnetic stimulation device of claim 17, wherein the applicatorcomprises a chair.
 23. A magnetic stimulation device, comprising: aconnection to an energy source; an energy storage device coupled to theenergy source; and a coil disposed within a casing and coupled to theenergy storage device, wherein the energy storage device is configuredto discharge a plurality of energy pulses to the coil to generate pulsesof a time-varying magnetic field, wherein the energy storage device isin a serial connection with the coil, and wherein the pulses of thetime-varying magnetic field have a time duration that corresponds to atime duration of the energy pulses discharged to the coil.
 24. Themagnetic stimulation device of claim 23, further comprising a controlunit, wherein the control unit is configured to assemble the pulses ofthe time-varying magnetic field into at least one of a triangular,rectangular, or exponential shape.
 25. The magnetic stimulation deviceof claim 23, further comprising a switching device in a parallelconnection to the energy source.
 26. The magnetic stimulation device ofclaim 23, wherein the coil comprises a litz-wire.
 27. The magneticstimulation device of claim 23, wherein the coil is configured togenerate the pulses of the time-varying magnetic field with a repetitionrate in a range of 50 Hz to 200 Hz.
 28. The magnetic stimulation deviceof claim 23, further comprising a blower configured to direct air overat least an upper and a lower side of the coil.
 29. The magneticstimulation device of claim 23, wherein the casing comprises an airoutlet on an upper side of the casing.
 30. The magnetic stimulationdevice of claim 23, wherein the coil is attached to the casing by aflexible fastening point configured to enable a cooling fluid to flowbetween the coil and the casing.
 31. The magnetic stimulation device ofclaim 23, wherein the energy storage device is configured to be chargedto thousands of volts.